Most evangelical Christians identify King Solomon as the most-likely author of Proverbs 17:9. Key points behind that view and its implications:

Who is the likely author
– Biblical attribution: Proverbs opens with “The proverbs of Solomon” (Proverbs 1:1) and many of the short, pithy sayings in the book are traditionally ascribed to him (e.g., Proverbs 10:1, 25:1). Proverbs 17:9 falls within that Solomonic material.
– Solomon’s reputation: Scripture describes Solomon as uniquely gifted with wisdom by God (1 Kings 3:5–14; 4:29–34; 2 Chronicles 1:7–12), which gives biblical reason to attribute wise sayings to him.
– Historical and church tradition: Jewish and Christian tradition from early times has treated much of Proverbs as Solomon’s work. Evangelical scholarship commonly accepts Solomonic authorship for the bulk of the book, while recognizing the book is a compilation.

Evangelical perspective on authorship and inspiration
– Many evangelicals hold that Solomon either wrote or was the source/compiler of these proverbs and that he did so under divine inspiration (cf. 2 Timothy 3:16). That means the sayings are seen as authoritative, wise guidance given through a God‑appointed wise king.
– At the same time, evangelicals also acknowledge the book is a collection: some portions explicitly come from other authors (e.g., Agur in ch. 30, Lemuel in ch. 31), and later editors may have arranged and preserved the material.

A brief note on Proverbs 17:9
– The verse (NIV): “Whoever would foster love covers over an offense, but whoever repeats the matter separates close friends.”
– This reflects core Solomonic/wisdom themes: the value of discretion, love expressed in forgiveness, and the social consequences of gossip or needless repetition. Evangelicals often connect such proverbs to New Testament teaching on forgiveness and reconciliation (e.g., Matthew 18:21–22; Ephesians 4:29–32).

If you want more: recommended readings from an evangelical angle include the Proverbs treatments in reputable commentaries (e.g., John MacArthur, Derek Kidner, or the Expositor’s Bible Commentary) and the biblical passages cited above (Proverbs 1; 1 Kings 3).